Technical Field
The present invention relates to a mask, and in particular relates to a mask with excellent Bacterial Filtration Efficiency (BFE) and low breathing resistance.
Related Art
Generally, masks are designed so as to cover the nose and the mouth for the purpose of preventing bacteria, viruses and the like from entering, and preventing penetration of blood.
In general, such masks usually have a 3 layer configuration including an outer layer, a filter layer, and an inner layer (Japanese Patent Application Laid-Open (JP-A) No. 61-272063).
The main purpose of the outer layer is to protect the filter layer, however it may for example be colored to make it fashionable, and a spunbond nonwoven fabric such as polypropylene is generally employed for the outer layer.
The filter layer is the most important material configuring the mask, and functions to filter out bacteria, viruses, pollen and the like. The filter layer is accordingly generally designed by employing fine diameter fibers such that foreign objects do not readily pass through, whilst air passes through easily. There are also filter layers designed such that foreign objects adhere through static electricity by statically charging the filter layer (JP-A No. 61-272063).
The inner layer is positioned on the side of the mouth of the wearer, and is a portion that makes direct contact with the skin of the wearer. The inner layer is accordingly designed so as not to cause skin irritation through contact. Generally, materials such as thermal bonded nonwoven fabric, mixed material papers made from a mixture of pulp and polyester fibers, and rayon papers are employed for the inner layer.
Recently, masks are being sold that have new styles of filter layer for increasing the filtration efficiency against bacteria, viruses and the like, and for reducing breathing resistance.
There are also masks employing multiple layers of nonwoven fabrics, for example a 3 layer structure of spunbond/melt blown/spunbond nonwoven fabrics (Japanese National-Phase Publication No. 2001-515237).
However, for general purpose masks, attempts to increase the filtration efficiency against foreign objects makes it necessary to make the filter layer thicker, or to add new nonwoven fabric layers to the filter layer, with the issue arising that breathing resistance increases, resulting in difficulty in breathing with prolonged wearing. As a result, the wearer may occasionally remove the mask to recover their breath, dramatically reducing the efficiency of the mask.
Moreover, there is also an issue that since there is a large variability in the grammage of nonwoven fabrics configuring the filter layer, there is a possibility in masks for which blood fluid impermeability is demanded that blood penetration occurring at portions where the grammage of nonwoven fabric in the filter layer is low.
Since manufacturing methods of new style filter layers are very particular, controlling the performance thereof is difficult, with a large amount of variability both within the same batch and between batches compared to that of existing filter layers, and with a larger variability in the grammage of nonwoven fabrics than with existing filter layers. Accordingly, in attempting to secure filtration performance against foreign objects, excessive quality must be achieved, such that the use of such filters is unavoidably limited from a cost efficiency perspective.
There is also the issue that formability decreases, and productivity is reduced for example when the filter layer is made thicker and additional nonwoven fabric layers are introduced to the filter layer in order to increase filtration efficiency.
The present invention addresses the above issues, and an object thereof is to provide a mask with excellent filtration efficiency against foreign objects such as bacteria, viruses and pollen, with low breathing resistance, and with little variability in performance.